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Microscopic study of migration of microbes in food-packaging paper and board
I Suominen1, M L Suihko, M Salkinoja-Salonen
1University of Helsinki, Department of Applied Chemistry and Microbiology, Finland.
Abstract:
The microbiological barrier properties of food-packaging paperboards, coated with polyethylene, mineral pigment or a biodegradable polymer and of high-density paper were examined with confocal laser scanning microscopy. The results show that the spatial distribution of microscopically observable bacterial cells was uneven inside the paperboard. The concentration in the interface between the polyethylene coating and the cellulose fibers was 100-200 times higher than inside the cellulose matrix. The bacteria in the interface and the mineral coating layer grew in response to access to food and moisture, whereas no growth was observed inside the fiber web, not even after extended exposure for up to 90 days. The paper and paperboards studied contained soluble nutrients (C:N:P 54:9:1 to 309:3:1) and no measurable antimicrobial activity. The factor limiting growth and migration of bacteria inside the fiber web was most likely limited access to free water, even under conditions of extensive wetting. The studied paperboards functioned as efficient barriers against translocation of microbes. The microbes residing between the paperboard and its polymer coating facing food, was the only potential site from which microbes could leak into food. This emphasizes the need for high hygienic quality of surface-sizing chemicals. Mineral-coating pigments were a source of microbes and their application behind the PE coating facing food is contraindicated.
Insights
Food packaging paperboards effectively block microbes, but bacteria can thrive and migrate from the interface between coatings and paper. Limiting water access prevents growth within the fiber web, ensuring barrier integrity.
Area of Science:
- Food Science and Technology
- Microbiology
- Materials Science
Background:
- Food packaging paperboards are crucial for product safety.
- Understanding microbial behavior within paperboard structures is essential for preventing food contamination.
- Coating materials influence the barrier properties against microbial translocation.
Purpose of the Study:
- To evaluate the microbiological barrier properties of various food-packaging paperboards.
- To investigate the spatial distribution and growth of bacteria within paperboard structures.
- To identify potential microbial leakage pathways and factors limiting bacterial growth.
Main Methods:
- Confocal laser scanning microscopy was used to visualize bacterial cells within paperboard samples.
- Analysis of nutrient content (C:N:P ratios) and antimicrobial activity.
- Exposure studies up to 90 days under wetting conditions.
Main Results:
- Bacterial concentration was significantly higher (100-200x) at the interface between polyethylene coating and cellulose fibers compared to the fiber matrix.
- Bacteria in the interface and mineral coating layers showed growth with access to nutrients and moisture.
- No bacterial growth was observed within the fiber web, even after 90 days, likely due to limited free water.
- Paperboards demonstrated efficient barrier properties against microbial translocation.
Conclusions:
- The interface between paperboard and polymer coatings is a critical site for microbial proliferation.
- Limited water availability is the primary factor inhibiting bacterial growth within the fiber web.
- Hygienic quality of surface-sizing chemicals is paramount to prevent microbial leakage into food.
- Mineral-coating pigments can be a microbial source and should not be applied on the food-facing side of PE coatings.